1. Field of the Invention
This invention relates to a distance distribution measuring method, and in particular to a method of optically measuring the distribution of distances to objects in an ambient environment. Such a distance distribution measuring method is effectively utilized, for example, as visual means for the recognition of the environment of an automatically moving robot.
2. Related Background Art
As a method of optically measuring the distance to an object, there is a method called the stereo method. In this method, two objective lenses of the same focal length are maintained with their optic axes kept parallel to each other and juxtaposed with a predetermined distance therebetween. Illumination distribution measuring means is disposed rearwardly of each objective lens, whereby the distance to the object can be calculated from the positional relation between the identical illumination distribution patterns measured by the two measuring means.
FIGS. 1A and 1B of the accompanying drawings illustrate the principle of the stereo method. In these figures, the referece numerals 101 and 102 designate light-converging objective lenses equal in focal length, and the reference characters 101A and 102A denote the optic axes of these objective lenses, respectively. The lenses 101 and 102 are disposed so that their optic axes 101A and 102A are parallel to each other, and a straight line pass through the centers of the lenses (the base line) orthogonal to the optic axes 101A and 102A. Measuring means 103 is disposed rearwardly of the lens 101 at a location spaced from the lens by an amount corresponding to the focal length F of this lens, and measuring means 104 is disposed rearwardly of the lens 102 at a location spaced from the lens by an amount corresponding to the focal length F. These measuring means are disposed on a straight line extending in a direction parallel to the direction of the base line of the lenses 101 and 102.
In FIG. 1A, an object 105 exists at infinity in the direction of the optic axis 101A. In this case, the image 106 of the object 105 formed on the measuring means 103 by the lens 101 exist on the optic axis 101A and likewise, the image 107 of the object 105 formed on the measuring means 104 by the lens 102 exists on the optic axis 102A.
In FIG. 1B, the object 105 exists at a location on the optic axis 101A which is spaced from the lens by a finite distance X. In this case, the image 106 of the object 105 formed on the measuring means 103 by the lens 101 exists on the optic axis 101A, while the image 107 of the object 105 formed on the measuring means 104 by the lens 102 exists at a location spaced apart by a distance D from the optic axis 102A.
Accordingly, by detecting the amount of deviation D of the image 107 from the optic axis 102A by the measuring means, the distance X to be measured can be found from the distance F between the lenses 101, 102 and the measuring means 103, 104 and the length L of the base line by a calculating process using the following equation: EQU X=FL/D.
Now, images are generally formed on and throughout the measuring means and it is difficult to specify the image of the same object point on the same object. So, in the stereo method as described above, the correlation between the illumination distribution on one measuring means 103 and the illumination distribution on the other measuring means 104 is taken to find the positions of the images 106 and 107 by the measuring means 103 and 104.
The applicant has already disclosed several techniques of measuring the distance distribution to various objects existing in multiple directions by carrying out such correlation processing of the illumination distributions or by other techniques in U.S. application Ser. Nos. 706,727, No. 796,313, No. 827,016 and No. 938,562.
FIGS. 2A, 2B and 2C of the accompanying drawings illustrate the principle of the above-described correlation method.
As the measuring means 103 and 104, use is made, for example, of CCD arrays which are self-scanning type sensors.
In FIG. 2A, a CCD array 103 which is the measuring means corresponding to the lens 101 has n light-receiving elements, and a CCD array 104 which is the measuring means corresponding to the lens 102 has m light-receiving elements (m&gt;n). That is, if the distance to the object on the optic axis 101A is to be measured, the image 106 by the lens 101 exists on the optic axis 101A independently of the distance to the object, while the image 107 by the lens 102 changes its position in conformity with the distance to the object and therefore, more light-receiving elements are provided on the CCD array 104 than on the CCD array 103. In such an arrangement, the CCD array 103 is referred to the standard view field and the CCD array 104 is referred to as the reference view field.
The illumination distributions in the standard view field and the reference view field as shown in FIG. 2A are such as shown in FIG. 2B. That is, the imaging relation in the direction of the optic axis between the object 105 and the image 106 with respect to the lens 101 is equal to the imaging relation in the direction of the optic axis between the object 105 and the image 107 with respect to the lens 102 (that is, the magnifications are equal) and therefore, the illumination distribution of the image 106 and the illumination distribution of the image 107 differ from each other only in that they deviate from the optic axis by a distance D.
Accordingly, the outputs corresponding to the respective light-receiving elements as shown in FIG. 2C are obtained from the CCD arrays 103 and 104.
So, to take the correlation between the outputs of the two CCD arrays, the sum of the differences between the corresponding ones of the outputs S(1)S(n) of the first to nth light-receiving elements in the standard view field and the outputs R(1) - R(n) of the first to nth light receiving elements in the reference view field, ##EQU1## is first found. Subsequently, in the same manner, the sum of the differences between the corresponding ones of the outputs S(1) - S(n) of the first to nth light-receiving elements in the standard view field and the outputs R(2) - R(n+1) of the second to (n+1)th light-receiving elements in the reference view field, ##EQU2## is found. Thereafter, in the same manner, up to ##EQU3## are found.
The number of COR which is the smallest one (ideally 0) of the (m-n+1) values found in this manner is chosen and that number is multiplied by the width of a light-receiving element of the CCD array, whereby the value of said D can be found.
Now, in the correlation method as described above, where the object images on the CCD arrays 103 and 104 are, for example, repetitive pattern images or the like, it is sometimes judged that when the correlation is taken, there is correspondence even at a wrong position, and this leads to the problem that the accuracy of measurement is not yet sufficient. Also, where a distance measurement is effected with respect to each direction to find the distance distribution to the objects in the field of view, there arises the problem that the number of correlation calculations becomes very great and the processing circuit of the measuring apparatus becomes complicated. Further, there is also the problem that in the correlation method, the resolutions of direction cannot be sufficiently enhanced.